The present invention generally relates to a drive control system for a vehicle with an auxiliary driving system. In particular, the present invention relates to a drive control system on a vehicle having an electric motor auxiliary driving system for reducing roll-back when the vehicle is starting motion on a hill or for propelling the vehicle in stop-and-go traffic.
A common problem for an operator of a vehicle that is stopped on an incline or hill is that the vehicle is susceptible to rolling backwards when the operator removes his or her foot from the brake. This problem is especially evident in a vehicle with a manual transmission, although, an operator of a vehicle with an automatic transmission can also experience roll-back to a lesser extent.
Where a manual transmission is employed, the operator of a vehicle starting on a steep slope initially engages both the brake pedal and the clutch pedal and places the vehicle in gear. The operator then moves his or her right foot from the brake pedal to the accelerator pedal and engages the accelerator pedal while releasing the clutch pedal with his or her left foot. If the operator does not perform this operation skillfully and carefully, the operator may experience the unpleasant and undesirable sensation of rolling backwards or even stalling the engine. Additionally, if the accelerator pedal is not applied quickly enough, backward motion can cause the vehicle to roll into another vehicle immediately behind it in traffic.
To address this problem, numerous braking systems, sometimes referred to as “hill-holders,” have been developed to arrest backward motion of a vehicle starting on a hill when the operator removes his or her foot from the brake pedal. Prior art “hill-holders” generally disclose clutch or friction brake mechanisms that mechanically restrict vehicle drivelines or the vehicle's wheels to prevent roll-back.
Conventional “hill holder” systems are supplementary mechanisms that increase the cost of the vehicle and complicate manufacture and assembly. Additionally, conventional mechanical mechanisms of this type can cause lurching or uneven acceleration of the vehicle if the brake mechanism of the system disengages improperly after the accelerator pedal has been engaged.
Another common problem experienced by an operator of a vehicle with a manual transmission occurs in stop-and-go traffic such as during rush hour or during city driving. In stop-and-go traffic, the operator must repeatedly engage and release the clutch pedal over a short distance. This repetitive motion can cause strain and discomfort to the operator.
Vehicles with auxiliary driving systems provide a means for reducing roll-back without the need for conventional mechanical “hill holder” systems and can propel a vehicle in stop-and-go traffic without repetitive clutch pedal engagement. Vehicles with auxiliary driving systems generally contain two separate power sources for driving the wheels of the vehicle. A typical configuration for a vehicle with an auxiliary driving system is a vehicle with an internal combustion engine as the power source for a primary driving system and an electric motor as the power source for the auxiliary driving system. The auxiliary driving system can provide on-demand torque delivery to the wheels of the automobile. This provides on-demand four wheel drive capability which promotes stability during slip events. The auxiliary driving system can also be utilized to increase acceleration of the vehicle when desired.